Defoliating cotton plants with bis-xanthates



United States Patent 3,011,887 DEFOLIATING COTTON PLANTS WITH BlS-XANTHATES Harold E. Cnpery and Norman E. Searle, Wilmington,

Del., assignors to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Substituted for abandoned application Ser. No. 351,038, Apr. 24, 1953. This application June 26, 1958, Ser. No. 744,659

3 Claims. (Cl. 712.7)

This invention relates to compositions and methods for defoliating plants.

In the growing of plant crops, there frequently occurs a need to defoliate the plant. For example, in the growing of cotton plants at the time the bolls are ripening and ready to open, defoliation of the plant not only permits access of the sun to dry the bolls on the lower part of the plant but it also permits more efiicient picking of the bolls whether by hand or by machine, prevents staining of the cotton from leaves crushed during picking, and deprives the boll weevel and cotton aphids of their food supply so that the defoliation process thereby reduces the number of these pests which survive to cause damages in the following year.

We have now found that effective defoliation is obtained thru the use of bisxanthates. Unlike most materials heretofore suggested for defoliant use, the bisxanthates cause the leaves to drop while still living instead of requiring complete kill of the foliage before abscission. Thus there is obtained more complete defoliation because of the avoidance of adherence of dead leaves to the plant which frequently results from rapid killing of the leaves before abscission.

The bisxanthate compounds employed in the compositions and methods of the invention can be represented by the formula P.0o-s-A-so'o- R' The radical linking the two xanthate groups, that is, the radical represented by the letter A in the above formula is a divalent hydrocarbon radical having an aliphatic carbon atom linkage to the sulfur atom of each xanthate radical. Thus, for example, A can be an alkylene radical such as methylene, ethylene, propylene, hexamethylene, decamethylene, and the like; an alkylidene radical such as ethylidene, and propylidene; an unsaturated aliphatic hydrocarbon divalent radical such as 1,4-but-2-enylene and similar olefinic or acetylenic radicals; an aralkylene radical such as para-xylylene; and an aralkylidene radical such as benzylidene. Preferably, the linking group A is alkylene, and still more preferably, it is lower alkylene, that is, alkylene containing from 1 to 6 carbon atoms.

R and R in the above formula represent organic radicals linked to the oxygen atoms thru a carbon atom. These organic radicals can be varied widely. R and R' can be alkyl, aryl, aralkyl, alkaryl, cycloaliphatic, and they can contain unsaturated linkages. Preferably R and R are alike and are alkyl or alkenyl.

' The bisxanthates employed in'the compositions and methods of the invention are obtained by reacting an alkali metal xanthate with a dibromo compound in the presence of a solvent as will be shown more particularly in the detailed examples to follow.

Examples illustrating the bisxanthate compounds employed in the compositions and methods of the invention are:

Methylene bismethylxanthate Methylene bisethylxanthate Methylene bisisopropylxanthate Methylene bis-n-propylxanthate Methylene bisallylxanthate Methylene bis-n-butylxanthate Methylene bisisobutylxanthate Methylene bis-sec.butylxanthate Para-xylylene bis-n-propylxanthate Hexamethylene bis-n-propylxanthate 1,4-but-2-enylene bis-ethylxanthate The defoliant compositions of the invention are prepared by admixing the bisxanthates with a material of the kind commonly designated in the herbicide and pest control art as an adjuvant, carrier, or diluent. These added materials are sometimes called fluent carriers since they aid in adapting the composition for ready application through suitable jets, nozzles, spreaders, and similar devices commonly used in applying pest control compositions and the like. In other words, the bisxanthate is mixed with an additional material or materials of the kind known in art to provide a formulation adapted for ready application by ordinary means.

The dusts, solvents, liquid diluents, wetting, dispersing and emulsifying agents referred to in US. Patent 2,426,-

417 as insecticidal adjuvants can be employed in the' preparation of the defoliant compositions of the present invention. Other wetting, dispersing, and emulsifying agents such as those listed in detail in Bulletin E-604 of the Bureau of Entomology and Plant Quarantine of the US. Department of Agriculture and such as those set out in the book by McCutcheon entitled Synthetic. Detergents (McNair-Dorland, 1950) can also be used.

Dust compositions of the invention contain a bisxanthate mixed with a finely divided carrier or dust such as talc, pyrophyllite, natural clay, diatomaceous earths, and other powdered diluents such as those set out in the aforementioned U.S. patent.

Liquid compositions of the invention contain a bisxanthate, either homogeneously dispersed in water or nonsolvent carriers, or dissolved in a solvent. To secure homogeneous dispersions in non-solvent liquid diluents, a surface-active agent of the wetting, dispersing, or emulsifying type is used. In fact, the preferred defoliant formulations of the invention, whether in liquid or solid form, contain the active ingredient homogeneously admixed with such a surface-active agent. Generally, the wetting, dispersing or emulsifying agent will not comprise more than about 5 to 15% by weight of the formulation, and with the better surface-active adjuvant materials the percentage will be 5 or less. Usually, the minimum lower concentration will be 0.1%

The defoliant compositions are applied either as a spray or a dust to the foliage to be removed in accordance with conventional defoliant application practices. The active ingredients are, of course, applied in amount sufficient to exert the desired defoliant action. The dosage or rate of application of the defoliant formulations of the invention will vary somewhat depending upon the particular bisxanthate employed and other factors such as the size of the plants, the luxuriance of the foliage, and the like.

The bisxanthates are, however, extremely effective defoliants at low rates of application; For example, tests with compositions of the invention containing various bisxanthates have been found to effect from about to defoliation within ten days after application to four to six month old cotton plants (plants that have quit blooming and are setting bolls) when applied at a dosage corresponding to about eight pounds per acre of the bisxanthate. Under idea conditions, lesser amounts can be used and, in general, an application of from about two to twenty pounds per acre of the active ingredient is preferred for defoliation of cotton plants.

positions which are The invention is further illustrated by reference to the following examples in addition to the examples given above. Parts are parts by weight.

EXAMPLE 1 Methylene bisethylxantlzate 'Methylene bisethylxanthate was prepared by the reaction of methylene bromide with potassium ethylxanthate in acetone.

To a solution of 26.1 parts of methylene bromide in 120 parts acetone, there was added 50.4 parts of potassium ethylxanthate with stirring and sulficient cooling to maintain the temperature at 2027 C. After 1.75 hours, the reaction was completed as indicated by the change in color from yellow to white.

The reaction mixture was mixed with 600 parts water, cooled, and crystals separated. The crystals were slurried in 49 parts methanol, filtered, washed with cold methanol to give 32.5 parts of white crystalline methylene bisethylxanthate' which melted at 3633 C. Upon recrystallization from n-hexane, the crystals melted at 39-40" C.

Analysis.-Calcd for (DJ-1 3 S, 56.00. Found: S, 50.30.

The compound of this example was soluble in the common organic solvents including hydrocarbons.

By an analogous method, the compounds given in Ex amples 2 thru 7 below were prepared. The bisxanthates of these examples were obtained as oils which were isolated in methylene chloride solution from which they were recovered by topping in vacuo. They are not distilled and hence the results given are not those of the highly refined products.

Table Sulphur Analysis Example Compound m,

V Calcd Found Methylene bismethylxanthatm 1 6387 '56. 2 57. 71 Methylene bis-n-propylranthate- 1. 5893 45. 10 45. 42 Methylene bisisopropylxanthate 1. 5840 45. 10 45. 44 Methylene bis-n-butylxanthate. 1. 5734 41. 41.07 Methylene biiso'outylxanthata 1. 5710 41. 05 42.02 Methylene bis-sec. hut-ylxanthate- 1.5706 41.05 41. 26

EYAMPLE 8 Hydrocarbon oil formulation in a refined kerosene in the following proportions by Weight. 7 a l 25% methylene bis-n-propylxanthate 20% ethylene oxide-sperm oil alcohol reaction product (surface-active agent) 55% refined kerosene 'Ihe emulsifiable oil concentrate of this. example is readily dispersible in water to obtain aqueous spray com- A highly efiective in application as defoliants. 1

4 EXAMPLE 10 Dust formulation A defoliant dust is prepared by admixing methylene bisethylxanthate, prepared according to Example 1, with talc in the proportions of about 9 parts by weight of tale for each part by weight of the bisxanthate.

The dust composition of this example is free flowing and is easily broadcast over plants which are to be defoliated.

EXAMPLE 11 Water dispersible formulation A water dispersible defoliant powder is obtained by admixing methylene bisisobutylxanthate with finely divided fullers earth and bentonite in the following proportions by weight:

10% methylene oisisobutylxanthate 5% bentonite fullers earth The water dispersible powdered formulation of this example is free flowing and is easily dispersed in water to give a relatively stable suspension in an aqueous spray composition. I

The defoliant compositions of the invention can include, if desired, other biologically active materials, for example, herbicides such as Z-(p-chlorophenyl)-1,1-dimethyl urea and other pest control materials such as insecticides and fungicides so that the benefits of various materials can be obtained in a single application in accordance with conventional spray or dust application practices in the agricultural field.

Theembodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 7

1. A method for defoliating cotton plants which comprises applying to the foliage, in amount sufficient to effect defoliation, an organo-bisxanthate having the formula R0-( isAs( i-0R' wherein A is a divalent hydrocarbon radical of up to and including 12 carbon atoms and having an aliphatic carbon atom linkage to the sulfur atom of each xanthate radical and R and R are hydrocarbon radicals selected from the class consisting of lower alkyl and lower alkenyl radicals.

. 2. A method for defoliating cotton plants which con prises applying to the foliage of the plants, in an amount suificient to effect defoliation, an alkylene bis-lower alkylxanthate, said alkylene having up to and including 12 carbon atoms.

3. A method for defoliating cotton plants which comprises applying to the foliage of the plants, in an amount sufiicient to effect defoliation, methylene bis-n-propyl xanthate.

References Cited inthe file of this patent OTHER REFERENCES V Kosternaya: Chemical, Abstracts, vol. 33, col. 3760(6), 1939. Beilsteins Handbuch der Organischen Chemie, -1s supplement to the 4th edition, vol. VI, pp. 46 and 50. 

1. A METHOD FOR DEFOLIATING COTTON PLANTS WHICH COMPRISES APPLYING TO THE FOLIAGE, IN AMOUNT SUFFICIENT TO EFFECT DEFOLIATION, AN ORGANO-BUZXANTHATE HAVING THE FORMULA 